The invention relates to a module for measuring tire pressure, especially used for measuring the air pressure inside a tire of a motor vehicle so as to warn the conductor of a dangerous underinflation or overinflation of the tire.
In general, the pressure measurement module is fastened to the rim of the tire and comprises, in a case, a pressure sensor with an air inlet, a card supporting a printed circuit, the sensor being mounted on said card, and a communication channel between the air inlet of the sensor and the inside of the tire, all these components being embedded in a vibration-resistant protective encapsulating resin. The sensor and the channel both bear against the card supporting the printed circuit, on each side of the card, in line with an opening passing through the card.
The pressure measurement module is exposed to environmental attack from rain, soap, dust, carbon particles and above all blowout-repair products. There is a risk of all these agents contaminating, or even obstructing, the air inlet of the pressure sensor and consequently damaging the sensor. In particular, blowout-repair products, generally silicone-based, are injected in liquid form into the tire should the latter suffer a blowout, and then they cure and solidify under the action of the air pressure, thus obstructing all the orifices, including the air inlet of the pressure sensor. Furthermore, when manufacturing the sensor the protective encapsulating resin is poured in the form of a liquid with a very low viscosity, so that if the sealing in the mating plane between the printed-circuit board and the channel and in the mating plane between the printed-circuit board and the sensor is insufficient, there is also the risk of the air inlet being obstructed by the resin.
In short, there is a not insignificant risk of contamination, or even of obstruction, of the air inlet of the pressure sensor in pressure measurement modules of the prior art. The present invention aims to reduce this drawback.
For this purpose, the invention relates to a pressure measurement module comprising an air pressure sensor, with an air inlet, and an anti-contamination filter for protecting the air inlet, characterized in that the sensor is mounted on a card for supporting a printed circuit, the filter extends through said card and a contact surface is provided between the filter and the sensor, forming a single sealing surface helping to seal the air inlet.
Thanks to the filter, impurities and liquids are prevented from getting near to the air inlet of the sensor and the number of sealing surfaces is reduced compared with the pressure measurement modules of the prior art. The filter, since it helps to seal, consequently has a sealing function.
In a preferred embodiment, the filter is attached to the sensor by an impermeable adhesive.
Also preferably, the filter is external to the sensor.
Advantageously, the sensor and part of the filter are embedded in a protective encapsulating resin which acts as a brace, pressing the filter against the sensor.
During manufacture of the sensor, the filter is pressed against the sensor by the action of a thrust spring and the resin is injected in liquid form. After the resin has solidified and the spring has been removed, the solidified resin maintains the compressive force, thus ensuring that the filter is pressed against the sensor. This further improves the sealing of the junction between the filter and the sensor.
Also advantageously, the filter is made of a hydrophobic material.
Finally, the filter preferably has a convex free surface for air intake.
The convex shape of the air intake surface of the filter helps to expel the impurities, their expulsion being assisted by the centrifugal force, and furthermore allows the air intake surface to be easily cleaned, by simply scraping it.